Technical Field
The present invention relates to a phase adjusting circuit having a function of adjusting phases, and also relates to an inverter circuit and a power supply system, which use the phase adjusting circuit.
Related Art
Inverter circuits are used, for example, for motors or high-frequency power generators to generate alternating current with desired frequency from direct current or alternating current. In the case where the load connected to the inverter circuit is a resonant load, the resonant frequency of the load may change. In order to prevent a reduction in the conversion efficiency of the inverter circuit, the inverter circuit is provided with a circuit for adjusting oscillation frequencies so as to follow the resonant frequency of the load. A known circuit for adjusting oscillation frequencies is described, for example, in Japanese Patent Application Laid-open No. 2005-318509.
However, with the known method of adjusting oscillation frequency, in the case where the resonant frequency largely changes (for example, in the case where the resonant frequency changes from the minimum value to the maximum value within the variable frequency of an inverter), a gap arises between the oscillation frequency of the inverter circuit and the resonant frequency of the load, causing a problem of deterioration in conversion efficiency of the inverter circuit. Such a gap results from variations in performance of, for example, parts constituting the load, the inverter circuit, and the oscillation-frequency adjusting circuit itself, and the degree of the gap varies individually.
The present invention has been made in view of the points described above, and an object of the present invention is to provide a phase adjusting circuit, an inverter circuit, and a power supply system, which can highly precisely adjust frequencies throughout the entire range of frequencies to be dealt with.